The present invention relates to an optical filter comprising a transparent support and a filter layer. In more detail, the invention relates to an optical filter used in a display device such as a plasma display panel (PDP), a liquid crystal display device (LCD), an electroluminescence display (ELD), a fluorescent indicator tube or a field emission display to prevent a remote-control from faulty working and to improve the color reproducibility of the display.
A display device such as a liquid crystal display (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), a cathode-ray tube (CRT), a fluorescent indicator tube or a field emission display displays a color image with a combination of the three primary colors (i.e., red, blue, green). However, it is very difficult (practically impossible) to use the ideal three primary colors. For example, the plasma display panel uses phosphors of the three primary colors, which emit light containing an unnecessary component (in the wavelength region of 500 to 620 nm).
Therefore, it has been proposed to correct the color balance of the displayed image by using an optical filter absorbing the unnecessary component. The optical filter for the color correction is described in Japanese Patent Provisional Publication Nos. 58(1983)-153904, 61(1986)-188501, 3(1991)-231988, 5(1993)-205643, 9(1997)-145918, 9(1997)-306366 and 10(1998)-26704.
Further, it has been reported that infrared rays (mainly in the wavelength region of 750 to 1,100 nm) emitted from the display device may cause faulty working of a remote control using an infrared ray. For solving this problem, an infrared rays-absorbing filter is used. Dyes used in the infrared rays-absorbing filter are described in U.S. Pat. No. 5,945,209.
An object of the present invention is to provide an optical filter selectively removing infrared rays.
Another object of the present invention is to provide an optical filter selectively removing light impairing the color purity of displayed images as well as the infrared rays.
A further object of the invention is to provide a plasma display panel that does not cause faulty working of a remote control.
A furthermore object of the invention is to provide a plasma display panel improved in balance of a displayed image.
The present invention provides an optical filter which comprises a transparent support and a filter layer, wherein the filter layer has at least three absorption maximums in the wavelength region of 750 to 1,100 nm, each of said three absorption maximums is in the wavelength regions of 750 to 850 nm, 851 to 950 nm, and 951 to 1,100 nm.
The invention also provides a plasma display panel having a display surface covered with an optical filter which comprises a transparent support and a filter layer, wherein the filter layer has at least three absorption maximums in the wavelength region of 750 to 1,100 nm, each of said three absorption maximums is in the wavelength regions of 750 to 850 nm, 851 to 950 nm, and 951 to 1,100 nm.